# Plunger Pull

Document Sample

```					                                              										Plunger	Pull
Students observe that air exerts pressure.

Related Web Pages for Students
•		http://eo.ucar.edu/kids/sky/index.htm
•		http://eo.ucar.edu/webweather/
•		http://www.ucar.edu/learn

Directions
1.		Put	the	plungers	together,	with	concave	sides	facing	one	another.
Student Learning                          2.		Notice	that	they	touch	but	do	not	hold	together.
Objectives                                3.		Put	the	plungers	firmly	together,	with	concave	sides	facing	one
•			Students	learn	that	air	exerts        					another	again,	put	this	time	push	the	air	out	that	is	held	and	shared
pressure	at	14.7	pounds	per          					between	them.		Notice	what	happens.
column	inch	at	sea	level	on          4.		Hold	the	plungers	by	their	outside	ends	and	try	to	pull	them	apart.
average	(1	kg	per	sq.	cm.)           					Do	not	twist	or	peel	them,	just	pull.		Are	you	able	to	pull	them	apart?
•			Students	learn	that	a
vacuum	is	an	area	of				             Ask yourself the following questions:
empty	space.                         1.		Is	suction	a	force?	If	not,	what	causes	it?
2.		How	much	weight	is	exerted	on	the	plungers	from	air	pressure?
How	would	you	go	about	determining	this	quantity?
Time
•	     10	minutes,	activity;
Background Information
10	minutes,	discussion
Although	air	is	invisible,	it	still	takes	up	space	and	has	weight.		In	fact,	it
may	surprise	you	to	know	that	air	weighs	14.7	pounds	per	column	inch
Materials                                 at	sea	level,	or	put	another	way,	over	2,100	pounds	per	column	cubic
For	each	pair	of	students:                foot!		Wow!		The	reason	we	don’t	feel	its	weight	is	because	air,	like	all
•		One	set	of	suction	cups                fluids,	doesn’t	just	push	down.	Instead,	it	pushes	in	all	directions.
or	plungers,	any	size.                Water	has	weight	too,	but	you	aren’t	crushed	when	you	swim	to	the	bot-
Wooden	handles	are	best	              tom	of	a	deep	pool	because	water,	like	air,	also	pushes	in	all	directions.
to	remove.                            But	just	try	to	lift	all	that	water	you’re	swimming	under.		It	weights	over
62	pounds	per	cubic	foot!
National Standards
•				A:	Science	as	Inquiry                In	1654,	Otto	von	Guerick	performed	a	demonstration	similar	to	this
•				D:	Earth	Science                     activity	with	the	plungers.		He	used	two	metal	hemispheres	that	were
22	inches	in	diameter	and	placed	them	together	in	the	shape	of	a	single
sphere.		He	had	invented	the	world’s	first	vacuum	pump	shortly	before
1654,	which	pumped	air	out	of	his	sphere	instead	of	into	it.		When	he
did	so,	the	two	hemispheres	held	together	tightly.		No	human	could	pull
Otto’s	sphere	apart,	so	in	front	of	Emperor	Ferdinand	III	of	Prussian
Saxony	(now	Germany)	and	many	others,	he	attached	two	eight-horse
Otto von Guerick’s sphere is         teams	to	each	end	of	his	sphere.		Despite	a	great	effort,	the	horses
known around the world as            could	not	pull	his	sphere	apart.		Afterall,	they	were	trying	to	pull	apart
the Madgeburg Sphere                 nearly	3	tons!
because it was built in
Guerick’s home-town of               When	air	is	inside	the	sphere,	it	exerts	the	same	amount	of	force	as	the
Madgeburg in what today is           air	on	the	outside	of	the	sphere.		When	you	remove	the	air	inside	of	the
Germany.                             sphere,	however,	the	air	on	the	outside	presses	the	two	halves	of	the
sphere	together.		If	you	peel	the	plungers	apart	slightly	and	let	air	back
inside,	the	sphere’s	two	sides	will	no	longer	stick	together!	The	force	on
the	inside	and	outside	will	once	again	be	the	same.
4.

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